1. Field of the Invention
The present invention relates to a microphotographing apparatus which can photograph a sample observed through an eyepiece of a microscope, and more particularly to improvement of photometry for measuring the brightness of a desired portion of an object to be photographed.
2. Description of the Related Art
Generally known is a fluorescence microscope for observing a fluorescent sample of a protein or gene in which a fluorescent marker is added to an organic tissue or cell.
Recently, by a phase contrast microphotography or a differential interfere microphotography, or the combination thereof, it have been possible to stain a substance having only minute fluorescence in multicolor so as to accurately detect the positional relationship between the substance and another substance or to observe where the fluorescent colored substance is located in the cell structure.
In many cases of the above-mentioned fluorescent observation, a fluorescent portion is present in a limited portion of a dark background. To photograph such a fluorescent portion, it is necessary to measure the brightness of the image to be photographed in order to determine the exposure time.
According to the conventional photometry, an exposure time is determined on the basis of an average brightness in the field of a microscope. This method has a drawback that the fluorescent portion is lost in the photographed image.
To overcome this drawback, for example, Published Unexamined Japanese Patent Application (PUJPA) No. 58-214121 proposes an apparatus for observing a photometry region (a region the brightness of which is to be measured) through an eyepiece of a microscope, measuring the brightness of a desired portion of the observed portion, and determining the exposure time on the basis of the brightness data on the photometry region.
FIG. 10 shows an optical system of the microphotographing apparatus disclosed in the above mentioned application. A light beam is applied through a objective lens 1 to a first surface S1 of a quadrilateral prism 2, and output from a second surface S2 of the prism 2, which is parallel to the first surface S1. The light beam is reflected by first to third reflecting members Ml to M3 in sequence. The beam reflected by the third reflecting member M3 is incident on a third surface S3 of the quadrilateral prism 2 and output through a fourth surface S4 thereof. Then, the beam is guided to an eyepiece 3.
A reticle R for focusing the beam on an object and a photometry member 4 having a inclined semi-transparent portion for reflecting the beam are arranged between the second and third reflecting members M2 and M3. With this arrangement, an intermediate image Il is formed on the reticle R.
A relay lens 5 is provided on the outgoing side of the photometry member 4, so that the intermediate image Il formed on the reticle R is re-formed as an object image I2 before the eyepiece 3.
In the above-described optical system, the photometry member 4 (i.e. photometry prism) having a semi-transparent plane, which reflects a portion of the light beam corresponding to a photometry region, is movable with respect to the optical axis. By virtue of the photometry member 4, an indicator image indicating the photometry region is projected on the object image observed through the eyepiece 3 The indicator image is movable to a desired position on the object image by moving the photometry member 4 in a plane perpendicular to the optical axis.
The image in which the photometry region is designated is extracted from, for example, a first reflecting member Ml, to determine the exposure time. When the image is photographed, the second reflecting member M2 is removed from the light path, an intermediate image I3 is formed on a film via a relay lens 6 and a shutter 7 is controlled in accordance with the exposure time.
However, in the above photographing apparatus, an intermediate image Il is formed in the observing optical system and the reticle R for indicating a photometry region and the range of a photograph is provided in the observing optical system and the photographing optical system so that the user can observe the photometry region and the range of a photograph. For this reason, the relay lenses 5 and 6 are required for relaying the intermediate images 11 and 13, with the result that an observed image and a photographed image are degraded.